Low density filler material has been of interest to cigarette manufacturers because it provides a way of reclaiming and using tobacco dust and other scrap tobacco in the manufacture of cigarettes. The low density filler material displaces an equal volume of higher density cut tobacco filler thus resulting in a lower "tar" and nicotine cigarette. Low density cigarette filler material has usually been of two different types, namely, an extruded mixture of tobacco dust, starch and a binder or a roasted grain.
Cured tobacco leaf usually undergoes several processing steps prior to the time the resulting cut filler is used to make cigarettes. The normal sequence is to separate the stem from the laminae of the cured tobacco leaf. The tobacco laminae undergoes further processing steps finally resulting in cut filler and the stems are either discarded or employed in the manufacture of reclaimed tobacco products. The storing, handling, cutting, blending and transporting stages of conventional cigarette making results in the formulation of a considerable amount of wasted tobacco material in the form of dust and fines. This cigarette dust and fines (C-dust) is of such small size as to be useless as cut filler for cigarettes. However, it is possible to retrieve C-dust and fines and employ this material either with tobacco stems or alone in the manufacture of reclaimed or reconstituted tobacco. The use of C-dust or C-dust and stems has also been suggested for use in extruded tobacco products.
The extrusion of tobacco particles, starch and a binder has been previously described in the patent literature. For example, in U.S. Pat. No. 4,823,817, the use of cellulose binders, such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose and hydroxypropyl cellulose, with starch and tobacco is disclosed. In U.S. Pat. No. 4,880,018, galactomannans, such as locust bean gum and tara gum, and mixtures of galactomannans with carrageens and xanthan gum as binders with tobacco particles and optional filler material are disclosed.
According to the extrusion process of the aforementioned U.S. Pat. No. 4,823,817, starch, tobacco offal and binder are dry mixed, then fed into the hopper of a twin screw extruder. Sufficient water is fed into the barrel of the extruder to moisten the mixture of tobacco, starch and binder. The mixture is then extruded at a pressure sufficient to keep the water in the liquid phase and at a sufficiently high temperature so as to gelatinize the starch. As the extrudate issues from the die, the water flashes into steam, thereby expanding the extrudate and forming a closed cell extrudate structure. The extruded material is then cooled and drawn down by counter-rotating rollers to form a sheet. The sheet is then slit into filaments which are used as a substitute for cut filler.